/* -*- P4_16 -*- */

#include <core.p4>
#include <v1model.p4>

// Constants
const bit<8>  TCP_PROTOCOL = 0x06;
const bit<16> TYPE_IPV4 = 0x800;
const bit<19> DEFAULT_ECN_THRESHOLD = 10;

// Custom types
typedef bit<9>  egressSpec_t;
typedef bit<48> macAddr_t;
typedef bit<32> ip4Addr_t;

// Header definitions
header ethernet_t {
    macAddr_t dstAddr;
    macAddr_t srcAddr;
    bit<16>   etherType;
}

header ipv4_t {
    bit<4>    version;
    bit<4>    ihl;
    bit<6>    diffserv;
    bit<2>    ecn;
    bit<16>   totalLen;
    bit<16>   identification;
    bit<3>    flags;
    bit<13>   fragOffset;
    bit<8>    ttl;
    bit<8>    protocol;
    bit<16>   hdrChecksum;
    ip4Addr_t srcAddr;
    ip4Addr_t dstAddr;
}

header congestion_digest_t {
    bit<32>    switch_id;
    bit<32>    port;
    bit<32>    queue_depth;
    bit<32>    ecn_marked_count;
}

struct metadata {
    bit<1>     congestion_detected;
    bit<19>    congestion_qdepth;
}

struct headers {
    ethernet_t         ethernet;
    ipv4_t             ipv4;
    congestion_digest_t digest;
}

/*************************************************************************
*********************** P A R S E R  ***********************************
*************************************************************************/

parser MyParser(packet_in packet,
                out headers hdr,
                inout metadata meta,
                inout standard_metadata_t standard_metadata) {

    state start {
        transition parse_ethernet;
    }

    state parse_ethernet {
        packet.extract(hdr.ethernet);
        transition select(hdr.ethernet.etherType) {
            TYPE_IPV4: parse_ipv4;
            default: accept;
        }
    }

    state parse_ipv4 {
        packet.extract(hdr.ipv4);
        transition accept;
    }
}

/*************************************************************************
************   C H E C K S U M    V E R I F I C A T I O N   *************
*************************************************************************/

control MyVerifyChecksum(inout headers hdr, inout metadata meta) {   
    apply {  }
}

/*************************************************************************
**************  I N G R E S S   P R O C E S S I N G   *******************
*************************************************************************/

control MyIngress(inout headers hdr,
                  inout metadata meta,
                  inout standard_metadata_t standard_metadata) {
    
    action drop() {
        mark_to_drop(standard_metadata);
    }
    
    action ipv4_forward(macAddr_t dstAddr, egressSpec_t port) {
        standard_metadata.egress_spec = port;
        hdr.ethernet.srcAddr = hdr.ethernet.dstAddr;
        hdr.ethernet.dstAddr = dstAddr;
        hdr.ipv4.ttl = hdr.ipv4.ttl - 1;
    }
    
    table ipv4_lpm {
        key = {
            hdr.ipv4.dstAddr: lpm;
        }
        actions = {
            ipv4_forward;
            drop;
            NoAction;
        }
        size = 1024;
        default_action = NoAction();
    }
    
    apply {
        if (hdr.ipv4.isValid()) {
            ipv4_lpm.apply();
        }
    }
}

/*************************************************************************
****************  E G R E S S   P R O C E S S I N G   *******************
*************************************************************************/

control MyEgress(inout headers hdr,
                 inout metadata meta,
                 inout standard_metadata_t standard_metadata) {
    
    action mark_ecn(bit<2> ecn_value) {
        hdr.ipv4.ecn = ecn_value;
        meta.congestion_detected = 1;
        meta.congestion_qdepth = standard_metadata.enq_qdepth;
    }
    
    action prepare_congestion_digest() {
        hdr.digest.setValid();
        hdr.digest.switch_id = 1;
        hdr.digest.port = (bit<32>)(standard_metadata.egress_port);
        hdr.digest.queue_depth = (bit<32>)(meta.congestion_qdepth);
        hdr.digest.ecn_marked_count = 1;
    }
    
    table ecn_config {
        key = {
            hdr.ipv4.ecn: exact;
        }
        actions = {
            mark_ecn;
            NoAction;
        }
        const default_action = NoAction();
    }
    
    table congestion_digest {
        key = {
            meta.congestion_detected: exact;
        }
        actions = {
            prepare_congestion_digest;
            NoAction;
        }
        const default_action = NoAction();
    }
    
    apply {
        if (hdr.ipv4.isValid() && (hdr.ipv4.ecn == 1 || hdr.ipv4.ecn == 2)) {
            if (standard_metadata.enq_qdepth >= DEFAULT_ECN_THRESHOLD) {
                ecn_config.apply();
            }
        }
        
        if (meta.congestion_detected == 1) {
            congestion_digest.apply();
        }
    }
}

/*************************************************************************
*************   C H E C K S U M    C O M P U T A T I O N   **************
*************************************************************************/

control MyComputeChecksum(inout headers hdr, inout metadata meta) {
    apply {
        update_checksum(
            hdr.ipv4.isValid(),
            {
                hdr.ipv4.version,
                hdr.ipv4.ihl,
                hdr.ipv4.diffserv,
                hdr.ipv4.ecn,
                hdr.ipv4.totalLen,
                hdr.ipv4.identification,
                hdr.ipv4.flags,
                hdr.ipv4.fragOffset,
                hdr.ipv4.ttl,
                hdr.ipv4.protocol,
                hdr.ipv4.srcAddr,
                hdr.ipv4.dstAddr
            },
            hdr.ipv4.hdrChecksum,
            HashAlgorithm.csum16
        );
    }
}

/*************************************************************************
***********************  D E P A R S E R  *******************************
*************************************************************************/

control MyDeparser(packet_out packet, in headers hdr) {
    apply {
        packet.emit(hdr.ethernet);
        packet.emit(hdr.ipv4);
        packet.emit(hdr.digest);
    }
}

/*************************************************************************
***********************  S W I T C H  *******************************
*************************************************************************/

V1Switch(
    MyParser(),
    MyVerifyChecksum(),
    MyIngress(),
    MyEgress(),
    MyComputeChecksum(),
    MyDeparser()
) main;